Internet Access Technologies

Context: FIT1047_MOC · how an end user’s device physically joins an ISP and becomes part of the Internet · the “last mile” technologies

Quick Revision

• 🎯 Objective: end user makes a physical connection to an ISP ➔ ISP authenticates, assigns an IP, and tells the device its router + DNS ➔ device can send/receive packets.
• ⚡ Key Constraint: know each technology’s medium + rough speed and the two key acronyms — ADSL is asymmetric (more download than upload, ends at a DSLAM); NBN uses a GPON fibre backbone with several last-mile options.

📝 Access basics

• Physical connection ➔ to the ISP network via ADSL / NBN / 4G etc.
• ISP steps ➔ authenticate (security + billing) → assign an IP address → inform the device of the router IP and DNS servers → device becomes part of the Internet.

🔌 The four technologies

1. Dial-up modem

• Modulator / Demodulator ➔ converts digital data ↔ analog “sound” sent over the telephone copper voice band.
• Speed ➔ max 54 kbit/s (occupies the phone line — no simultaneous calls).

2. ADSL (Asymmetric Digital Subscriber Line)

• Compromise ➔ reuse existing telephone copper but use the full bandwidth (0–1104 kHz), not just the 4 kHz voice band.
• Frequency split ➔ 0–4 kHz voice, ~25–138 kHz upstream, ~138–1104 kHz downstream → split into 4 kHz sub-bands (“247 modems”); bad channels are simply dropped.
• Asymmetric ➔ far more download than upload (upload limited by crosstalk/noise at the DSLAM); up to ~24 Mbps.
• Setup ➔ a filter (splitter) separates voice + data at the home; the line runs to the DSLAM (DSL Access Multiplexer) — modem + switch — at the telephone exchange.
• Last mile ➔ the most expensive part of rollout (an individual cable to every customer).
• Extensions ➔ VDSL (cancels DSLAM crosstalk, up to ~100 Mbps); Fibre-to-the-Node (FTTN) shortens the copper run (node <1 km away).

3. NBN (National Broadband Network, Australia)

• Backbone ➔ fibre-optic GPON (Gigabit Passive Optical Network) — uses unpowered optical splitters (cheaper, more reliable; downstream broadcast).
• Customer connections ➔ Fibre-to-the-Premises (FTTP), FTTN/curb (+VDSL/HFC), fixed wireless (LTE), satellite (remote).
• Wholesale model ➔ NBN owns/operates the network; Retail Service Providers (RSPs) sell to customers via ~121 Points of Interconnect (PoI); the customer end is a Network Termination Device (NTU).

4. Mobile data (4G / 5G)

• Cellular ➔ ISP-operated antennas split an area into cells (few hundred m in cities → up to 100 km rural); seamless roaming between cells; IP-based.
• 4G ➔ frequencies ~450 MHz–5 GHz; ~100 Mbit/s (theoretical up to 1 Gbit/s).
• 5G ➔ up to 10 Gbit/s (usually ~1 Gbit/s); higher frequencies (24–54 GHz) → more bandwidth but shorter range → smaller cells; aims: fast + low-latency, reliable, massive device counts (IoT); competes with fixed NBN.
• Growth ➔ mobile is ~⅓ of Internet traffic, driven by smartphone apps + video.

⚠️ Common Mistakes

• 💡 “Asymmetric” = the A in ADSL ➔ download bandwidth ≫ upload; the asymmetry is caused by crosstalk at the DSLAM, not a marketing choice.
• 💡 DSLAM vs filter ➔ the filter/splitter is at the home (separates voice+data); the DSLAM is at the exchange (aggregates many lines). Don’t swap them.
• 💡 Higher 5G frequency ⇒ shorter range ➔ more bandwidth but needs more, smaller cells — a direct physics trade-off.

🧠 Active Recall

Why did ADSL win the early broadband market despite fibre being faster?

Answer

• Short answer: the last mile is the most expensive part of any rollout, and ADSL reused the copper telephone cables already installed to every home, avoiding new cabling.
• Why: Full-bandwidth reuse ➔ ADSL exploits the whole 0–1104 kHz range of existing copper (splitting into 4 kHz sub-bands) instead of laying fibre to each premises.